Lubricant composition

ABSTRACT

A marine diesel cylinder lubricant composition having a total base number of at least 30. The composition includes at least 40 weight per cent of an oil of lubricating viscosity, at least one detergent prepared from at least two surfactants, preferably phenate and sulphonate surfactants, at least one boron-containing dispersant providing at least 100 ppm of boron, and at least one zinc-containing antiwear additive, preferably a zinc dihydrocarbyl dithiophosphate, providing at least 230 ppm, preferably at least 250 ppm, of zinc. The marine diesel cylinder lubricant composition exhibits reduced wear even when used with high sulphur fuels.

This invention concerns a lubricant composition, in particular, a marinediesel cylinder lubricant (MDCL) composition. Marine diesel cylinderlubricant compositions are total loss lubricants and their purpose is toprovide a strong oil film between the cylinder liner and the pistonrings and to neutralise acids formed by combustion of sulphur compoundsin the fuel.

Fuels used for diesel engines generally have a high sulphur content(such as, for example, at least 3.5 per cent sulphur), which results inexhaust gases from diesel engines containing large amounts of sulphuroxides (SO_(x)). The sulphur oxides react with moisture also present inthe exhaust gases to form sulphuric acid which corrodes the engine.Marine diesel cylinder lubricant compositions therefore includeoverbased metallic detergents to neutralise the sulphuric acid.Commercial marine diesel cylinder lubricant compositions generally havea total base number (‘TBN’) of at least 70 (as determined using ASTMD2896).

Environmental concerns have prompted many areas, such as coastal areas,to require the use of low sulphur fuels, i.e. fuels including less than1.00 per cent by weight of sulphur, which allows the use of marinediesel cylinder lubricant compositions having lower total base numberssuch as, for example, 40. This therefore creates the need for ships tocarry tanks for two different lubricants.

U.S. Pat. No. 4,842,755 discloses a marine diesel cylinder lubricanthaving a base number of at least 60. The composition includes a boratedashless dispersant, one or more overbased metal compounds and a zincdialkyl dithiophosphate providing 0.02 to 0.023 weight per cent (200-230ppm) of zinc. The specific examples show that increasing the amount ofzinc above 230 ppm results in a loss in performance benefits in ring andliner wear.

An aim of the present invention is to provide a marine diesel cylinderlubricant composition having a total base number of at least 30,preferably 35 or more (ASTM D 2896-01), that is suitable for use withboth high and low sulphur fuels.

A further aim of the present invention is to provide a marine dieselcylinder lubricant composition having a total base number of at least30, preferably 35 or more (ASTM D 2896-01), that is suitable for usewith both high and low sulphur fuels, whilst still providing therequired level of protection against corrosive wear when used with ahigh sulphur fuel.

In accordance with the present invention there is provided a marinediesel cylinder lubricant composition having a total base number, asdetermined according to ASTM D2896, of at least 30, preferably at least35 or more, and comprising:

-   -   at least 40 weight per cent, based on the total amount of the        marine diesel cylinder lubricant composition, of an oil of        lubricating viscosity,    -   at least one detergent prepared from at least two surfactants,        preferably phenate and sulphonate surfactants,    -   at least one boron-containing dispersant providing at least 100        ppm of boron, and    -   at least one zinc-containing antiwear additive, preferably a        zinc dihydrocarbyl dithiophosphate, providing more than 230 ppm,        preferably at least 250 ppm, of zinc.

The inventors have surprisingly found, considering the teachings of U.S.Pat. No. 4,842,755, that in a marine diesel cylinder lubricantcomposition including a detergent prepared from at least twosurfactants, the use of more than 230 ppm zinc provides increasedprotection against wear.

The inventors have also found that the marine diesel cylinder lubricantcomposition defined above provides a good level of wear protection evenat a low total base number, such as, for example, 40, when used with ahigh sulphur fuel.

In accordance with the present invention there is also provided a methodof operating a marine diesel engine, the method including the step ofusing the marine diesel cylinder lubricant composition defined above tolubricate the engine.

In accordance with the present invention there is also provided use ofthe marine diesel cylinder lubricant composition defined above to reducewear in a marine diesel engine.

Oil of Lubricating Viscosity

The oil of lubricating viscosity (sometimes referred to as lubricatingoil) may be any oil suitable for the lubrication of a marine engine. Thelubricating oil may suitably be an animal, a vegetable or a mineral oil.Suitably the lubricating oil is a petroleum-derived lubricating oil,such as a naphthenic base, paraffinic base or mixed base oil.Alternatively, the lubricating oil may be a synthetic lubricating oil.Suitable synthetic lubricating oils include synthetic ester lubricatingoils, which oils include diesters such as di-octyl adipate, di-octylsebacate and tridecyl adipate, or polymeric hydrocarbon lubricatingoils, for example liquid polyisobutene and poly-alpha olefins. Commonly,a mineral oil is employed. The lubricating oil may generally comprisegreater than 60, typically greater than 70, mass per cent of thecomposition, and typically have a kinematic viscosity at 100° C. of from2 to 40, for example for 3 to 15, mm²s⁻¹ and a viscosity index of from80 to 100, for example from 90 to 95.

Another class of lubricating oils is hydrocracked oils, where therefining process further breaks down the middle and heavy distillatefractions in the presence of hydrogen at high temperatures and moderatepressures. Hydrocracked oils typically have a kinematic viscosity at100° C. of from 2 to 40, for example from 3 to 15, mm²s⁻¹ and aviscosity index typically in the range of from 100 to 110, for examplefrom 105 to 108.

The oil may include ‘brightstock’ which refers to base oils which aresolvent-extracted, de-asphalted products from vacuum residuum generallyhaving a kinematic viscosity at 100° C. of from 28 to 36 mm²s⁻¹ and aretypically used in a proportion of less than 40, preferably less than 30,more preferably less than 20, mass per cent, based on the mass of thecomposition.

The marine diesel cylinder lubricant composition preferably includes atleast 50 weight per cent of oil of lubricating viscosity, morepreferably at least 60 weight per cent of oil of lubricating viscosity,even more preferably at least 70 weight per cent of oil of lubricatingviscosity, based on the total amount of the marine diesel cylinderlubricant composition.

Detergent Including at Least Two Surfactants

A detergent is an additive that reduces formation of piston deposits,for example high-temperature varnish and lacquer deposits, in engines;it has acid-neutralising properties and is capable of keeping finelydivided solids in suspension. It is based on metal “soaps”, that ismetal salts of acidic organic compounds, sometimes referred to assurfactants.

The detergent comprises a polar head with a long hydrophobic tail. Largeamounts of a metal base are included by reacting an excess of a metalcompound, such as an oxide or hydroxide, with an acidic gas such ascarbon dioxide to give an overbased detergent which comprisesneutralised detergent as the outer layer of a metal base (e.g.carbonate) micelle.

The detergent includes at least two surfactants, preferably at leastphenate and sulphonate surfactants. The detergent may be referred to asa complex/hybrid detergent. The complex detergent preferably includes atleast 5 mass per cent of phenate, more preferably at least 10 mass percent of phenate, based on the total amount of the detergent. The complexdetergent preferably includes at least 5 mass per cent of sulphonate,more preferably at least 8 mass per cent of sulphonate, based on thetotal amount of the detergent. The detergent preferably also includes asalicylate surfactant. The detergent preferably includes at least 5 massper cent of salicylate, more preferably at least 10 mass per cent ofsalicylate, based on the total amount of the detergent. The amount ofsurfactant in the complex detergent can be determined using techniquessuch as chromatography, spectroscopy and/or titration, well known topersons skilled in the art. The detergent may also include othersurfactants such as, for example, a thiophosphate, a naphthenate, or anoil-soluble carboxylate. The surfactant groups are incorporated duringthe overbasing process. The metal may be an alkali metal or an alkalineearth metal such as sodium, potassium, lithium, calcium and magnesium.Calcium is preferred.

Examples of complex detergents are described in WO 97/46643, WO97/46644, WO 97/46645, WO 97/46646 and WO 97/46647.

Preferably, the detergent has a TBN in the range of 250 to 500, morepreferably 280 to 480, even more preferably 300 to 450.

The marine diesel cylinder lubricant composition preferably includes atleast 2 weight per cent, preferably at least 5 weight per cent, morepreferably at least 8 weight per cent, of detergent including at leasttwo surfactants, based on the total amount of the marine diesel cylinderlubricant composition.

The marine diesel cylinder lubricant may also include further detergentssuch as a calcium phenate detergent, a calcium sulphonate detergent or acalcium salicylate detergent. The further detergent may have a low TBNof less than 50, a medium TBN ranging from 50 to 150 or a high TBN ofmore than 150. The marine diesel cylinder lubricant compositionpreferably includes at least 4 weight per cent, preferably at least 6weight per cent, of a further detergent, based on the total amount ofthe marine diesel cylinder lubricant composition.

Dispersant

The marine diesel cylinder lubricant composition includes at least onedispersant providing at least 100 ppm of boron. A dispersant is anadditive for a lubricating composition whose primary function incylinder lubricants is to accelerate neutralization of acids by thedetergent system.

A noteworthy class of dispersants are “ashless”, meaning a non-metallicorganic material that forms substantially no ash on combustion, incontrast to metal-containing, hence ash-forming, materials. Ashlessdispersants comprise a long chain hydrocarbon with a polar head, thepolarity being derived from inclusion of, e.g., an O, P or N atom. Thehydrocarbon is an oleophilic group that confers oil-solubility, havingfor example 40 to 500 carbon atoms. Thus, ashless dispersants maycomprise an oil-soluble polymeric hydrocarbon backbone having functionalgroups that are capable of associating with particles to be dispersed.

Examples of ashless dispersants are borated succinimides, e.g. boratedpolyisobutene succinic anhydride; and polyamine condensation productsthat are borated.

The marine diesel cylinder lubricant composition preferably includes atleast 150 ppm, more preferably at least 200 ppm, of boron, based on thetotal amount of the marine diesel cylinder lubricant composition.

Antiwear Additive

The antiwear additive provides at least 230 ppm, preferably at least 250ppm, of zinc, based on the total amount of the marine diesel cylinderlubricant composition. The antiwear additive preferably provides atleast 275 ppm, more preferably at least 300 ppm, even more preferably atleast 325 ppm, even more preferably at least 350 ppm, even morepreferably at least 375ppm and most preferably at least 385 ppm, ofzinc.

The antiwear additive may be prepared in accordance with knowntechniques by firstly forming a dihydrocarbyl dithiophosphoric acid(DDPA), usually by reaction of one or more alcohols or a phenol withP₂S₅ and then neutralizing the formed DDPA with a zinc compound. Forexample, a dithiophosphoric acid may be made by reacting mixtures ofprimary and secondary alcohols. Alternatively, multiple dithiophosphoricacids can be prepared comprising both hydrocarbyl groups that areentirely secondary and hydrocarbyl groups that are entirely primary. Tomake the zinc salt, any basic or neutral zinc compound may be used butthe oxides, hydroxides and carbonates are most generally employed.Commercial additives frequently contain an excess of zinc due to use ofan excess of the basic zinc compound in the neutralisation reaction.

The preferred zinc dihydrocarbyl dithiophosphates are oil-soluble saltsof dihydrocarbyl dithiophosphoric acids and may be represented by thefollowing formula:[(RO)(R¹O)P(S)S]₂Znwhere R and R¹ may be the same or different hydrocarbyl radicalscontaining from 1 to 18, preferably 2 to 12, carbon atoms and includingradicals such as alkyl, alkenyl, aryl, arylalkyl, alkaryl andcycloaliphatic radicals. Particularly preferred as R and R¹ groups arealkyl groups of 2 to 8 carbon atoms. Thus, the radicals may, forexample, be ethyl, n-propyl, l-propyl, n-butyl, l-butyl, sec-butyl,amyl, n-hexyl, l-hexyl, n-octyl, decyl, dodecyl, octadecyl,2-ethylehexyl, phenyl, butylphenyl, cyclohexyl, methylcyclopentyl,propenyl, butenyl. In order to obtain oil-solubility, the total numberof carbon atoms (i.e. in R and R¹) in the dithiophoshoric acid willgenerally be 5 or greater. The zinc dihydrocarbyl dithiophosphate cantherefore comprise zinc dialkyl dithiophosphates.

Anti-Oxidants

The marine diesel cylinder lubricant composition may include at leastone anti-oxidant. The anti-oxidant may be aminic or phenolic. Asexamples of amines there may be mentioned secondary aromatic amines suchas diarylamines, for example diphenylamines wherein each phenyl group isalkyl-substituted with an alkyl group having 4 to 9 carbon atoms. Asexamples of anti-oxidants there may be mentioned hindered phenols,including mono-phenols and bis-phenols.

Preferably, the anti-oxidant, if present, is provided in the compositionin an amount of up to 3 mass per cent, based on the total amount of themarine diesel cylinder lubricant.

Other additives such as pour point depressants, anti-foamants, and/ordemulsifiers may be provided, if necessary.

The terms ‘oil-soluble’ or ‘oil-dispersable’ as used herein do notnecessarily indicate that the compounds or additives are soluble,dissolvable, miscible or capable of being suspended in the oil in allproportions. These do mean, however, that they are, for instance,soluble or stably dispersible in oil to an extent sufficient to exerttheir intended effect in the environment in which the oil is employed.Moreover, the additional incorporation of other additives may alsopermit incorporation of higher levels of a particular additive, ifdesired.

The lubricant compositions of this invention comprise defined individual(i.e. separate) components that may or may not remain the samechemically before and after mixing.

The present invention is illustrated by, but in no way limited to, thefollowing examples.

EXAMPLES

Marine diesel cylinder lubricant compositions were prepared having TBNsof either 40 or 70. The lubricant compositions comprised: an overbasedcomplex calcium detergent including phenate and sulphonate surfactants;a calcium phenate having a base number of 250; a borated dispersant; andan anti-wear agent.

The lubricant compositions were subjected to the Bolnes Test using aBolnes crosshead engine (a single cylinder 2-stroke engine, the Bolnes3DNL), calibrated and stabilized, operating on a fuel including about3.5 per cent sulphur. The Bolnes engine speed was 500 rpm with alubricant feed rate of 1.00 g/kwh. Each lubricant composition was testedfor 96 hours. The test conditions were designed to create corrosive wearof the cylinder liner over this time. Wear was measured in microns inspecific calibrated places on the cylinder liner. The average recordedwear is reported below. The lower the recorded result, the less wear ofthe cylinder liner. Comparative Exam- Exam- Example 1 ple 2 ple 3Example 4 Example 5 Detergent 15.24 12.10 10.80 including at least twosurfactants Detergent 14.30 7.15 including at least two surfactants 250TBN 3.34 8.00 10.00 8.02 6.00 Calcium Phenate Detergent Borated 3.053.00 Dispersant Borated 3.00 2.67 2.00 Dispersant Antiwear 0.28 1.000.50 0.67 0.50 Agent Antioxidant 0.50 Base oils 78.09 75.90 75.20 74.3484.35 Base Number 70 70 70 70 40 (ASTM D 2896-01) Boron (ppm) 107 105390 347 260 Zinc (ppm) 216 770 385 516 385 Bolnes Test Liner Wear, 19 1011 12 12 average

The above table clearly shows that less wear is produced with marinediesel cylinder lubricants including 385 ppm or more of zinc when thedetergent is prepared from at least two surfactants. It is particularlysurprising that example 5, which has a TBN of 40, produces less wearwith the high sulphur fuel than comparative example 1 which has a TBN of70.

1. A marine diesel cylinder lubricant composition having a total basenumber of at least 30 and comprising: at least 40 mass per cent of anoil of lubricating viscosity, a detergent prepared from at least twosurfactants, a boron-containing dispersant providing at least 100 massppm of boron, and a zinc-containing antiwear additive.
 2. Thecomposition of claim 1 in which the detergent includes at least 5 massper cent of phenate and at least 5 mass per cent of sulphonate, based onthe total amount of the detergent.
 3. The composition of claim 1 inwhich the detergent includes a salicylate surfactant.
 4. The compositionof claim 1 in which the lubricant has a base number of at least
 35. 5.The composition of claim 1 in which the dispersant includes at least 150mass ppm of boron, based on the total amount of the composition.
 6. Thecomposition of claim 1 in which the antiwear additive includes at least275 mass ppm of zinc.
 7. The composition of claim 1 in which theantiwear additive is an oil-soluble salt of a dihydrocarbyldithiophosphoric acid represented by the following formula:[(RO)(R¹O)P(S)S]₂Zn where R and R¹ are the same or different hydrocarbylradicals containing from 1 to 18 carbon atoms.
 8. The composition ofclaim 1 which also includes an aminic or phenolic antioxidant.
 9. Amethod of operating a marine diesel engine including a cylinder, whichmethod comprises: fueling the engine with a fuel having a sulphurcontent of at least 3.0 mass per cent, and lubricating the cylinder witha marine diesel cylinder lubricant composition having a total basenumber of at least 30 and comprising: at least 40 mass per cent of anoil of lubricating viscosity, a detergent prepared from at least twosurfactants, a boron-containing dispersant providing at least 100 massppm of boron, and a zinc-containing antiwear additive.